<template>
  <div class="progress-bar" ref="progressBar" @click="progressClick">
    <div class="bar-inner">
      <div class="progress" ref="progress"></div>
      <div class="progress-btn-wrapper" ref="progressBtn"
             @touchstart.prevent="progressTouchStart"
             @touchmove.prevent="progressTouchMove"
             @touchend="progressTouchEnd"
      >
        <div class="progress-btn"></div>
      </div>
    </div>
  </div>  
</template>
<script type="text/ecmascript-6">
  import {prefixStyle} from 'common/js/dom'
  const progressBtnWidth=16
  const transform=prefixStyle('transform')
  export default{
    props:{
        percent:{
            type:Number,
            default:0
        }
    },
    watch:{
        percent(newPercent){
            if(newPercent>=0 && !this.touch.initiated){
                const barWidth=this.$refs.progressBar.clientWidth-progressBtnWidth
                const offsetWidth=newPercent*barWidth
                this.$refs.progress.style.width=`${offsetWidth}px`
                this.$refs.progressBtn.style[transform]=`translate3d(${offsetWidth}px,0,0)`
            }
        }
    },
    created(){
        this.touch={}
    },
    methods:{
        progressTouchStart(e) {
        this.touch.initiated = true
        this.touch.startX = e.touches[0].pageX
        // 当前移动的位置
        this.touch.left = this.$refs.progress.clientWidth
      },
      progressTouchMove(e) {
        if (!this.touch.initiated) return
        const deltaX = e.touches[0].pageX - this.touch.startX
        const offsetWidth = Math.min(Math.max(0, this.touch.left + deltaX), this.$refs.progressBar.clientWidth - progressBtnWidth)

        this._offset(offsetWidth)
      },
      progressTouchEnd() {
        this.touch.initiated = false
        this._triggerPercent()
      },
      progressClick(e){
          const rect =this.$refs.progressBar.getBoundingClientRect()
          const offsetWidth=e.pageX-rect.left
          this._offset(offsetWidth);
          //这里当我们点击 progressBtn的时候 e.offsetX获取不对
       // this._offset(e.offsetX)
        this._triggerPercent()
      },
      _triggerPercent(){
         const barWidth=this.$refs.progressBar.clientWidth-progressBtnWidth
         const percent=this.$refs.progress.clientWidth/barWidth
         this.$emit('percentChange',percent)
      },
      _offset(offsetWidth){
          this.$refs.progress.style.width=`${offsetWidth}px`
          this.$refs.progressBtn.style[transform]=`translate3d(${offsetWidth}px,0,0)`
      }
    }
  }
</script>
<style scoped lang="stylus">
  @import "~common/stylus/variable"

  .progress-bar
    height: 30px
    .bar-inner
      position: relative
      top: 13px
      height: 4px
      background: rgba(0, 0, 0, 0.3)
      .progress
        position: absolute
        height: 100%
        background: $color-theme
      .progress-btn-wrapper
        position: absolute
        left: -8px
        top: -13px
        width: 30px
        height: 30px
        .progress-btn
          position: relative
          top: 7px
          left: 7px
          box-sizing: border-box
          width: 16px
          height: 16px
          border: 3px solid $color-text
          border-radius: 50%
          background: $color-theme
</style>
